Abstract: Beam collimators which are used to remove the divergent energy during the beam operation, are the typical high heat flux (HHF) components of neutral beam injection (NBI) device, and their stable operation is essential to the safe operation of the high-power NBI system. Considering the operation requirements of the quasi-steady EAST NBI device, the structures of its beam collimators were designed, and the steady state thermal analysis of the preliminary design structure of the magnet entrance collimator was obtained by using FLUENT. The results show that the preliminary design scheme can meet the operation requirements of the quasi-steady EAST NBI system (4 MW, pulse length 100 s) under the given operating conditions. This paper provides a useful reference for other typical HHF component design and safe operation of the quasi-steady EAST NBI system.